Chemical Reactions

Chapter 10

Reactions and EquationsSection 1 The process by which the atoms of one or

more substances are rearranged to form different substances is called a chemical reaction (aka chemical change)

Chemical Reaction Indicators Temperature Change (Release/absorption of

energy) Color change Odor Gas formation Formation of a solid

Representing Chemical Reactions

Reactants- starting substances Products- substances that are formed

during the reaction

Reactant 1 + Reactant 2 Product 1 + Product 2

“react to produce” or

“yield”

Always written to the arrow’s left

Always written to the arrow’s right

Symbols used in Equations

Symbol Meaning

+ Separates two or more reactants or products

Separates reactants from products

(s) Identifies solid state

(l) Identifies liquid state

(g) Identifies gaseous state

(aq) Identifies water solution

Writing Equations

“Iron and chlorine react to produce iron (III) chloride”

Iron (s) + chlorine (g) iron (III) chloride (s) Fe (s) + Cl2 (g) FeCl3 (s)

Chemical Equation- statement that uses chemical formulas involved in a chemical reaction Shows the number of atoms of each reactant and

each product is equal on both sides of the arrow (balanced)

Practice Problems

Write skeleton equations for the following word equations

hydrogen (g) + bromine (g) hydrogen bromide (g)

carbon monoxide (g) + oxygen (g) carbon dioxide (g)

potassium chlorate (s) potassium chloride (s) + oxygen (g)

Page 282 4-6

Steps for balancing equations1. Write the skeleton equation for the

reaction. Make sure that the chemical formulas are correctly written. Show the physical states of all reactants and products.

2. Count the atoms of the elements in the reactants. If a reaction involves identical polyatomic ions in the reactants and products, count the ions as they are elements.

3. Count the atoms of the elements in the products.

4. Change the coefficients to make the number of atoms equal on both sides of the equations. NEVER change the subscript in a chemical formula to balance an equation because doing so changes the identity of the substance.

5. Write the coefficients in their lowest possible ratio. (whole numbers)

6. CHECK YOUR WORK!

Practice Problem

Sodium hydroxide and calcium bromide react to produce solid calcium hydroxide and sodium

bromide. (The reaction occurs in water)

Organizing Technique

Starting

Balanced

Add Coefficients

Practice Problems

Solid zinc and aqueous hydrogen sulfate react to produce hydrogen gas and aqueous zinc sulfate

Classifying Chemical ReactionsSection 2

Synthesis-whenever two or more substances combine to form a single product

Example: 4Fe(s) + 3 O2(g) 2Fe2O3 (s) General Equation:

element/compound + element/compound compound

A + B ABCombustion- a substance reacts with oxygen to

produce carbon dioxide and water Example: CH4(g) + 2O2(g) CO2(g) + 2 H2O(g)

General Equation: Organic Compound + Oxygen Carbon Dioxide + Water

Organic Compound + O2(g) CO2 (g) + H2O(g)

Combustion reactions- oxygen combines with a substance and releases energy in the form of heat and light

Decomposition-a compound breaks down into two or more elements or new compounds

Example: NH4NO3(s) N2O(g) + 2H2O(g) General Equation: compound two or more

elements/compound AB A + B

Practice Problems:Practice Problems:1.1. The solids aluminum and sulfur react to produce The solids aluminum and sulfur react to produce

aluminum sulfide.aluminum sulfide.

2.2. Ethane gas (CEthane gas (C22HH66) burns in air, producing carbon ) burns in air, producing carbon dioxide gas and water vapordioxide gas and water vapor

3.3. Nickel (II) hydroxide (s) decomposes to produce nickel Nickel (II) hydroxide (s) decomposes to produce nickel (II) oxide (s) and water. (II) oxide (s) and water.

Replacement ReactionsSingle Replacement-one element takes the place

of another element in a compound Example: Fe(s) + CuSO4(aq) FeSO4(aq) + Cu(s) General Equation: element A + compound BX compound AX + element B

A + BX AX + B

HAVE TO USE THE ACTIVITY SERIES TO SEE IF THE METAL WILL BE REPLACED.

IF METAL (A) IS LOCATED ABOVE METAL (B), IT WILL REPLACE IT. (IF NOT, WRITE NO REACTION (NR)

Practice Problems

K (s) + ZnCl2 (aq)

Cl2 (g) + HF (aq)

Fe (s) + CuSO4 (aq)

Double-Replacement ReactionsDouble Replacement- the positive portions for two

ionic compounds are interchanged Example: Pb(NO3)2 (aq) + 2KI (aq) PbI2 (s) +

2KNO3 (aq) General Equation: compound AB + compound

CD compound AD + compound CBAB + CD AD + CB

NOTE: A PRECIPITATE OR WATER MUST BE FORMED!! TO PREDICT THIS, USE THE SOLUILITY RULES TO SEE IF A PRECIPITATE IS FORMED, FOLLOW THE DIRECTIONS TO THE CHART FOR THE COMPOUNDS OF THE PRODUCTS FORMED

Practice Problems

1. Aqueous lithium iodide and aqueous silver nitrate react to produce solid silver iodide and aqueous lithium nitrate.

2. BaCl2(aq) + K2CO3 (aq)

Section Assessment

What are the five classes of chemical reactions?

Identify two characteristics of combustion reactions.

Compare and contrast single-replacement reactions and double-replacement reactions.

Reactions in Aqueous SolutionsSection 3

Review: solution = homogeneous mixture

Solutes- the particles dissolved in the solution

Solvent- water (in most cases)- what does the dissolving Aqueous solution- a solution in

which water is the solvent

When two aqueous solutions that contain ions as solutes are combined, the ions may react with one another. (double-replacement reaction occurs)

Three types of products form from the DR-reaction Precipitate (type of solid) Water Gas

Ionic Equations Complete Ionic Equation- show all of

the particles in a solution as they realistically exist

Spectator Ions- Ions that do not participate in a reaction

Net Ionic Equation- include only the particles that participate in the reaction (forming a precipitate, water and/or gas)

Example

Pb(NO3)2 (aq) + 2KI (aq) → 2KNO3 (aq) + PbI2 (s)

Pb(NO3)2 (aq) + 2KI (aq) → 2KNO3 (aq) + PbI2 (s)

1. Complete Ionic Equation: Pb+2

(aq)+ 2NO3-1

(aq)+ 2K+ (aq)+ 2I-(aq) 2K+(aq) + 2NO3(aq) + PbI2(s)

2. Cross out spectator ions

Pb+2(aq)+ 2NO3

-1(aq)+ 2K+ (aq)+ 2I-(aq) 2K+

(aq) + 2NO3(aq) + PbI2(s)

3. Net Ionic Equation Pb+2

(aq)+ 2I-(aq) PbI2(s)

Your turn!

Aqueous solutions of lithium sulfate and calciumnitrate are mixed, forming the precipitate calcium sulfate

Steps to remember:1. Write out complete balanced (DR) reaction (with states)2. Complete ionic equation3. Get rid of spectator ions4. Net ionic equation